<template>  
    <div class="pagination">
    <button @click="changepageno(pageNo-1)" :disabled="pageNo === 1">上一页</button>
    <button @click="changepageno(1)" v-show="StartEnd.start !== 1">1</button>
    <span v-show="StartEnd.start > 2">···</span>
    
    <!-- 连续分页 -->
    <button 
      @click="changepageno(index + StartEnd.start)" 
        :class="{active:pageNo === index + StartEnd.start}" 
        v-for="(n,index) in (StartEnd.end - StartEnd.start +1)" 
        :key="index"
    >
    {{ index + StartEnd.start}}
        <!-- {{ n + StartEnd.start -1 }} -->
    </button>
   
     <!-- 连续分页 -->
     
    <span  v-show="totalPage -1 > StartEnd.end"  >···</span>
    <button @click="changepageno(totalPage)"  v-show="StartEnd.end !== totalPage">{{ totalPage  }}</button>
    <button @click="changepageno(pageNo+1)" :disabled="pageNo === totalPage">下一页</button>
    
    <span>共 {{total}} 条</span>
  </div>
</template>

<script>

  export default {      
    name: "Pagination",    
    props:{
        total:{   //总数
            required:true,
            type:Number
        },
        pageSize:{   //每页展示数量化
            required:true,
            type:Number
        },
        pageNo:{   //当前页码
            required:true,
            type:Number
        },
        continues:{   //连续页数
            default:5,
            type:Number
        },
        changepageno:{
          type:Function,
          required:true
        }
    },
    computed:{
        //计算连续页码的 起始值 和 结束值
        StartEnd(){
            //解构
            let {pageSize,pageNo,continues,totalPage} = this;

            //  1. 创建 起始值  和 结束值
            let start;   
            let end;
            //2.计算
            //判断 当前的 continues >  totalPage
            if(continues > totalPage){
                start = 1;
                end = totalPage;
            }else{
                  // 公式：  （连续页码-1）/2
                start = pageNo -  (continues-1)/2;
                end = pageNo + (continues-1)/2; 
                //当正常计算的start的值 小于1，statr = 1
                if(start < 1){
                    start = 1;
                    end = continues;
                }
                //当正常计算的end的值 大于 totalPage
                if(end > totalPage){
                    start = totalPage-continues +1;
                    end = totalPage;
                }



            }

            //返回
            return {start,end}
        },
        //计算当前的总页数
        totalPage(){
            return Math.ceil(this.total / this.pageSize);
        }
    }

  };
</script>

<style lang="less" scoped>
  .pagination {
    text-align: center;

    button {
      margin: 0 5px;
      background-color: #f4f4f5;
      color: gray;
      outline: none;
      border-radius: 2px;
      padding: 0 4px;
      vertical-align: top;
      display: inline-block;
      font-size: 13px;
      min-width: 35.5px;
      height: 28px;
      line-height: 28px;
      cursor: pointer;
      box-sizing: border-box;
      text-align: center;
      border: 0;

      &[disabled] {
        color: #c0c4cc;
        cursor: not-allowed;
      }

      &.active {
        cursor: not-allowed;
        background-color: #c81623;
        color: #fff;
      }
    }

    span {
      display: inline-block;
      line-height: 28px;
      font-size: 14px;
      color: gray;
      vertical-align: middle;
    }
  }
</style>